1. Field of the Invention
The invention relates to a process for the preparation of polymeric condensates, in particular of aqueous solutions thereof, the products thus obtainable and their use.
2. Brief Description of the Prior Art
In the preparation of polymeric condensates in which the low molecular weight fractions are ineffective or only of little effect for the desired application, there is a continuing attempt to increase the fraction of higher molecular weight, effective polymers at the expense of the ineffective, low molecular weight polymers. A possible method for doing so is to subject these low molecular weight condensates to further condensation.
However, the disadvantage of this method is that, with the inevitably resulting distribution of the molecular weights, there is formed very high molecular weight polymers which no longer have an activity since they tend to gel and/or precipitate. The latter properties make the polymer mixture unusable to a high degree.
The prior art has often described a method in which condensation is operated up to the beginning of gelling or of precipitation, and the polymer mixture obtained is then freed from the ineffective, low molecular weight polymer fraction by means of membrane filtration (cf. WO-A 00/67 884, DE-A-19 600 366, U.S. Pat. No. 6,056,967 and EP-A-873 371). The low molecular weight fraction separated off can then be recycled to a polycondensation.
The disadvantage of this procedure is, inter alia, the wastewater load produced. It was therefore the object to provide an alternative preparation process for polycondensates without the disadvantages of the prior art.